Formation of isolation surrounding well implantation

ABSTRACT

Embodiments of present invention provide a method of making well isolations. The method includes forming a hard-mask layer on top of said substrate; forming a first resist-mask on top of a first portion of the hard-mask layer and applying the first resist-mask in forming a first type of wells in a first region of the substrate; forming a second resist-mask on top of a second portion of the hard-mask layer and applying the second resist-mask in forming a second type of wells in a second region of the substrate; applying the first and second resist-masks in transforming the hard-mask layer into a hard-mask, the hard-mask having openings aligned to areas overlapped by the first and second regions of the substrate; etching at least the areas of the substrate in creating deep trenches that separate the first and second types of wells; and filling the deep trenches with insulating materials.

BACKGROUND

The present invention relates generally to the field of semiconductordevice manufacturing and in particular relates to method of defining andforming well isolation surrounding implanted wells in a semiconductorsubstrate.

As demand for advanced semiconductor devices such as those being oftenused in smartphones and high-definition television (HDTV) sets, forexample, continues to soar and evolve, so do these semiconductor devicescontinue to scale down in size and scale up in functionality, andcomplexity of semiconductor manufacturing technologies continue tobecome more complicated.

For example, different types of semiconductor transistors may bemanufactured on a single wafer or substrate. These types of transistorsmay include n-type transistors, which are manufactured on p-type wellsor regions implanted with positive ions in a substrate, and p-typetransistors, which are manufactured on n-type wells or regions implantedwith negative ions in the same substrate. In order for the p-typetransistors and n-type transistors to function properly as they aredesigned to, without interfering each other, the p-type wells and n-typewells are generally isolated from each other by well isolations that aremade between the p-type wells and n-type wells. With the continued scaledown and so shrinkage of real estate for each devices, well isolationsare required to be formed in very limited spaces between p-type wellsand n-type wells. Moreover, these well isolations are preferably madewith as few additional manufacturing steps as possible.

SUMMARY

Embodiments of present invention provide a method of forming wellisolation surrounding p-type wells and n-type wells in a semiconductorsubstrate, and in particular in a substrate having fins formed thereinfor the formation of fin-type field-effect-transistors (FinFET). Themethod may include, for example, providing a semiconductor substrate;forming first and second hard-mask layers on top of the substrate;forming a first resist-mask above a first portion of the first hard-masklayer and a corresponding portion of the second hard-mask layer andforming a first type of wells in a first region of the substrate that isnot covered by the first resist-mask; forming a second resist-mask abovea second portion of the first hard-mask layer and forming a second typeof wells in a second region of the substrate that is not covered by thesecond resist-mask; transforming the first hard-mask layer into a firsthard-mask having openings aligned to areas overlapped by the first andsecond regions of the substrate; etching at least the areas of thesubstrate in creating deep trenches that separate the first and secondtypes of wells; and filling the deep trenches with insulating materials.

In one embodiment, transforming the first hard-mask layer into the firsthard-mask includes applying the first resist-mask in transforming thesecond hard-mask layer into a second hard-mask; and applying the secondhard-mask and the second resist-mask in transforming the first hard-masklayer into the first hard-mask, wherein the second resist-mask is formeddirectly on top of the first hard-mask layer.

According to one embodiment, the method may further include expandingthe openings of the first hard-mask horizontally in an isotropic etchingprocess selective to the second hard-mask and selective to the secondresist-mask.

According to another embodiment, the method may further include etchingareas of the substrate exposed by the expanded openings of the firsthard-mask in creating the deep trenches.

In one embodiment, the first-type of wells are wells implanted withnegative ions and the second-type of wells are wells implanted withpositive ions.

In another embodiment, applying the second hard-mask and the secondresist-mask in forming the first hard-mask includes selectively etchingthe first hard-mask layer in areas that are neither covered by thesecond hard-mask nor covered by the second resist-mask until thesubstrate underneath the first hard-mask layer is exposed.

In yet another embodiment, the first hard-mask layer is materiallydifferent from the second hard-mask layer and has different etchselectivity.

In one embodiment, forming the second resist-mask on top of the secondportion of the first hard-mask layer includes forming the secondresist-mask in a region not previously covered by the first resist-mask,the second portion of the first hard-mask layer being separated by athird portion of the first hard-mask layer, from the first portion ofthe first hard-mask layer.

In another embodiment, forming the first type of wells in the firstregion of the substrate includes performing a first ion-implantation inthe first region of the substrate that is not covered by the firstresist-mask.

In yet another embodiment, forming the second type of wells in thesecond region of the substrate includes performing a secondion-implantation in the second region of the substrate that is notcovered by the second resist-mask, the second type of wells havingoverlapping regions with the first type of wells in areas correspondingto the third portion of the first hard-mask layer.

In one embodiment, the first hard-mask layer is a nitride hard-masklayer and the second hard-mask layer is a poly-silicon hard-mask layer.

In another embodiment, the first hard-mask layer and the secondhard-mask layer are made of same material of nitride.

In yet another embodiment, the second hard-mask layer has a thicknessthat is equal or thicker than a thickness of the first hard-mask layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description of preferred embodiments, taken inconjunction with the accompanying drawings of which:

FIG. 1 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells according to one embodiment ofpresent invention;

FIG. 2 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 1, according to one embodiment of present invention;

FIG. 3 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 2, according to one embodiment of present invention;

FIG. 4 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 3, according to one embodiment of present invention;

FIG. 5 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 4, according to one embodiment of present invention;

FIG. 6 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 5, according to one embodiment of present invention;

FIG. 7 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 6, according to one embodiment of present invention;

FIG. 8 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 7, according to one embodiment of present invention;

FIG. 9 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 8, according to one embodiment of present invention;

FIG. 10 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 9, according to one embodiment of present invention;

FIG. 11 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 10, according to one embodiment of presentinvention;

FIG. 12 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 11, according to one embodiment of presentinvention;

FIG. 13 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 12, according to one embodiment of presentinvention;

FIG. 14 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 13, according to one embodiment of presentinvention;

FIG. 15 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells according to anotherembodiment of present invention;

FIG. 16 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 15, according to one embodiment of presentinvention;

FIG. 17 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 16, according to one embodiment of presentinvention;

FIG. 18 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 17, according to one embodiment of presentinvention;

FIG. 19 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 18, according to one embodiment of presentinvention;

FIG. 20 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 19, according to one embodiment of presentinvention;

FIG. 21 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 20, according to one embodiment of presentinvention;

FIG. 22 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 21, according to one embodiment of presentinvention;

FIG. 23 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 22, according to one embodiment of presentinvention; and

FIG. 24 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 23, according to one embodiment of presentinvention.

It will be appreciated that for purpose of simplicity and clarity ofillustration, elements in the drawings have not necessarily been drawnto scale. For example, dimensions of some of the elements may beexaggerated relative to those of other elements for clarity purpose.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of variousembodiments of the invention. However, it is to be understood thatembodiments of present invention may be practiced without these specificdetails.

In the interest of not obscuring presentation of essences and/orembodiments of the invention, in the following detailed description,some processing steps and/or operations that are known in the art mayhave been combined together for presentation and/or for illustrationpurpose and in some instances may have not been described in detail. Inother instances, some processing steps and/or operations that are knownin the art may not be described at all. In addition, some well-knowndevice processing techniques may have not been described in detail and,in some instances, may be referred to other published articles, patents,and/or published patent applications for reference in order not toobscure description of essence and/or embodiments of the invention. Itis to be understood that the following descriptions may have ratherfocused on distinctive features and/or elements of various embodimentsof the invention.

FIG. 1 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells according to one embodimentof present invention. More specifically, as being illustrated in FIG. 1in forming semiconductor device 100 a semiconductor substrate 101 may beprovided and one or more structures such as, for example, structures 102and 103 may be formed inside substrate 101 and/or in some instances ontop of substrate 101. Substrate 101 may be a silicon substrate, asilicon-germanium substrate, a silicon-on-insulator (SOI) substrate, andmay contain other suitable semiconductor materials. In some embodiments,structures 102 may be structures made in a fin-like or fin-type shapethat are formed to make fin-type field-effect-transistors, or FinFET, asis commonly referred to in the art. Structures 102 may therefore bereferred to hereinafter as fins 102. Fins 102 may be formed of materialthat is same as or different from substrate 101 and may be formed tohave a height approximate, for example, 80˜120 nm which may varydepending upon specific design aspects. Fins 102 may be surrounded byone or more local shallow isolations, such as structures 103 as beingdemonstratively illustrated in FIG. 1. The local shallow isolations maybe made of oxide, nitride, or other insulating materials. In general,structures 102 and 103 may be formed through suitable currently existingor future developed techniques including etching and/or deposition andmay be further processed, via for example a chemical-mechanic-polishing(CMP) process, to have a coplanar top surface 109 for further formationof device 100.

FIG. 2 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 1, according to one embodiment of present invention.For example, the method may include forming a hard-mask layer or, as inthe embodiment illustrated in FIG. 2, a composite hard-mask layer (112and 113) to cover top surface 109 of structures 102 and 103. Optionally,before forming this composite hard-mask layer, an oxide layer 111 with athickness around, for example, 2˜4 nm may be formed, such as throughdeposition, directly on top of surface 109. Oxide layer 111 is a thinscreen oxide and may be used for protecting the underneath silicon finsor silicon interface from, for example, nitride which sometimes couldcause dislocations of silicon inside the substrate.

The composite hard-mask layer may include a nitride hard-mask layer 112of about 25˜35 nm which is applied on top of oxide layer 111 or directlyon top of surface 109 if the optional oxide layer 111 is not used. Thecomposite hard-mask layer may also include a poly hard-mask layer 113,such as poly-silicon or other suitable materials as being describedbelow in more details. The poly hard-mask layer 113 may preferably havea thickness around, for example 15˜25 nm, and may be applied on top ofnitride hard-mask layer 112 through, for example, achemical-vapor-deposition (CVD) process. Poly hard-mask layer 113 may beused in a process in conjunction with a well-implantation process totransform the underneath nitride hard-mask layer 112 into a hard-mask,which in turn may be used as mask in creating isolations in substrate101 surrounding the wells created in the well-implantation process. Inview of the above purpose, other materials that are suitable as maskmaterials may be used for hard-mask layer 112 and/or 113.

FIG. 3 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 2, according to one embodiment of present invention.As being described above, in order to form wells either positive ornegative types, a photo-resist layer may be applied on top of polyhard-mask layer 113, for example, through a spin-on process andsubsequently the photo-resist layer may be exposed and developed into aresist-mask 121, as being illustrated in FIG. 3, through aphotolithographic patterning process. In combination with the type ofresist-developing agent being used, materials of either positive ornegative photo-resist may be used. Resist-mask 121 may cover portions ofpoly hard-mask layer 113 and corresponding areas of substrate 101underneath thereof where either negative wells (NW) or positive wells(PW) are to be formed. In the demonstrated example, areas of substrate101 not covered (thus exposed) by resist-mask 121 are assumed to beformed into negative wells and for this reason resist-mask 121 maysometimes be referred to as NW-mask 121. However, embodiments of presentinvention are not limited in this aspect and for example, as anotherembodiment, the areas of substrate 101 not covered by resist-mask 121may be formed into positive wells, in which case resist-mask 121 may bereferred to as PW-mask. Resist-mask 121 may sometimes be referred to asa first resist-mask 121.

FIG. 4 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 3, according to one embodiment of present invention.Specifically, the method includes removing portions of poly hard-masklayer 113 that are not covered by resist-mask 121 to transform polyhard-mask layer 113 into a poly hard-mask 113 a which inherentlyresembles the mask shape of resist-mask 121. In other words, while beingcreated for ion-implantation purpose in a well-formation process,embodiment of present invention applies resist-mask 121 as a mask informing poly hard-mask 113 a. Resist-mask 121 is used for both purposes.

More specifically, in forming poly hard-mask 113 a, the exposed portionof poly hard-mask layer 113 may be removed or etched away through, forexample, a reactive-ion-etching (RIE) process. As being described belowin more details with reference to FIG. 7, poly hard-mask 113 a may laterbe used, together with a second resist-mask, in transforming nitridehard-mask layer 112 into a nitride hard-mask 112 a that in turn is usedin the subsequent formation of isolations surrounding the wells insubstrate 101. Here it is to be noted that, according to an alternateembodiment, formation of poly hard-mask 113 a may be carried outfollowing the formation of negative wells in substrate 101, which isdescribed below in more details.

FIG. 5 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 4, according to one embodiment of present invention.As being noted above, this step may alternately be performed before theformation of poly hard-mask 113 a as being described above withreference to FIG. 4.

More specifically, ion-implantation 104 a may be performed at this stageto create, for example, negative wells 104 inside substrate 101 in areasnot covered or protected by first resist-mask 121. For example, negativeions such as phosphorus (P⁻) or arsenic (As⁻) may be implanted intoregions of substrate 101 to form negative or n-type wells 104. Dependingupon the design of devices, positive ions may be alternately used in theion-implantation process to create positive or p-type wells as analternative embodiment. The implantation may cause ions to penetratethrough nitride hard-mask layer 112 and the optional oxide layer 111 toreach deep into substrate 101. According to one embodiment, materialother than nitride may be used in replacement of nitride hard-mask layer112 so long as it does not present any substantial obstacle to theion-implantation process and is suitable to be used later as a mask forformation of well isolation inside substrate 101.

FIG. 6 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 5, according to one embodiment of present invention.More specifically, the method may include stripping off resist-mask 121and subsequently forming a second resist-mask 122 that substantiallycovers, but not entirely, the exposed nitride layer 112. For example,the formed resist-mask 122 may have an offset, on its edges, from polyhard-mask 113 a such that a gap 113 b, in the order of 5˜50 nm, iscreated that exposes portions of the underneath nitride hard-mask layer112. The gap 113 b may represent a width close to or slightly less thana width of well isolations to be formed between n-well (NW) and p-well(PW) later in substrate 101. This second resist-mask 122 may be formedthrough, for example, any well-known photolithographic patterningprocesses. According to one embodiment, in creating this secondresist-mask 122, a mask pattern complementary to the one used increating first resist-mask 121 may be used after the pattern size beingproperly scaled to leave the necessary gaps from poly hard-mask 113 a.

FIG. 7 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 6, according to one embodiment of present invention.For example, the method may include applying poly hard-mask 113 ajointly with the second resist-mask 122 to pattern underneath nitridehard-mask layer 112 into a mask. More specifically, portions of nitridehard-mask layer 112 may be selectively removed through, for example, anetching technique 114 such as a reactive-ion-etching (RIE) process,wherein the portions being removed are neither covered by poly hard-mask113 a nor by the second resist-mask 122. In other words, portions ofnitride hard-mask layer 112 that are exposed by the gaps 113 b betweenpoly hard-mask 113 a and second resist-mask 122 are removed. As aresult, the removal creates a nitride hard-mask 112 a with openings 112c in areas corresponding to areas of substrate 101 between n-type wellsand p-type wells. According to another embodiment, the creation ofnitride hard-mask 112 a may be performed at a later stage, such as afterion-implantation in forming p-type wells 105 which is described below inmore details with reference to FIG. 8, but before the stripping off ofthe second resist-mask 122.

FIG. 8 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 7, according to one embodiment of present invention.As being discussed above, this step may be performed before the creationof nitride hard-mask 112 a which employs both poly hard-mask 113 a andresist-mask 122 in the creation process.

More specifically, ion implantation 105 a may be performed at this stageto form positive or p-type wells in designated areas of substrate 101using the second resist-mask 122 as an implantation mask. For example,positive ions such as, for example, boron (B⁺) or gallium (Ga⁺) may beimplanted into areas of substrate 101 not covered by resist-mask 122 toform p-type wells 105. The implantation may cause the created p-typewells to have a certain level of overlap with existing n-type wells inareas of substrate 101 corresponding to areas of the gaps 113 b betweenpoly hard-mask 113 a and resist-mask 122. Dosage and duration ofimplantation, as well as energy of ions may be controlled, as is knownin the art, to achieve pre-determined depth and density of wells intosubstrate 101.

FIG. 9 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 8, according to one embodiment of present invention.After forming n-type wells (NW) and p-type wells (PW) in substrate 101,isolations such as trench isolations are subsequently formed to separatethese two types of wells. According to one embodiment of presentinvention, the method may include directly applying nitride hard-mask112 a as a template in creating deep trenches inside substrate 101,which naturally self-aligns itself to the edge of the NW's and PW's.According to another embodiment, as being demonstratively illustrated inFIG. 9, the openings 112 c in nitride hard-mask 112 a may optionally beexpanded laterally to some degree, such as around 2˜20 nm depending onthe fin pitch and other factors, in outward directions to become amodified nitride hard-mask 112 b. Nitride hard-mask 112 b may thus haveopenings 112 d that are sufficiently wide to ensure coverage ofsubstrate regions that are ion-implanted twice during both the NWformation and the PW formation. For example, the expansion of openings112 c in hard-mask 112 a may be made through an isotropic etching of thenitride hard-mask 112 a which may be selective to poly hard-mask 113 aas well as resist-mask 122.

FIG. 10 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 9, according to one embodiment of present invention.More specifically, after modifying hard-mask 112 a into hard-mask 112 bwith expanded or enlarged openings 112 d, the method includes removingresist-mask 122 to expose underneath portions of hard-mask 112 b. Theremoval of resist-mask 122 may be made through, for example, well knownphoto-resist stripping process, or by any other selective wet or dryetching processes.

FIG. 11 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 10, according to one embodiment of presentinvention. Following the removal of resist-mask 122, poly hard-mask 113a may be removed as well, leaving only nitride hard-mask 112 b coveringunderneath substrate 101 as well as fin structures 102 while regionsthat were double ion-implanted are exposed by the openings 112 d inhard-mask 112 b. The removal of poly hard-mask 113 a may be optional andaccording to one embodiment may be removed during a subsequent processof creating deep trenches 115 inside substrate 101, such creation ofdeep trenches being described below in more details with reference toFIG. 12.

FIG. 12 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 11, according to one embodiment of presentinvention. More specifically, using nitride hard-mask 112 b inprotecting regions of substrate 101 underneath thereof, the exposedportions of substrate 101 may be selectively etched 115, through forexample a RIE process, to create deep trenches 106 that would separatep-type wells 105 from n-type wells 104. The etching is generallydirectional, and may be performed sufficiently deep to cut throughisolation structures 103, into and beyond the ion-implanted regions madein substrate 101 for both the p-type 105 and n-type wells 104. Theresulting trenches 106 ensure that the two well regions are sufficientlyseparated from each other. Trenches 106 may preferably have straightsidewalls but in some embodiments may be in a trapezoidal shape due tothe nature of etching.

FIG. 13 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 12, according to one embodiment of presentinvention. Following the creation of deep trenches 106 in substrate 101,suitable insulating materials 107 such as oxide, nitride, and/or low-kdielectric materials may be deposited into deep trenches 106, althoughother suitable materials may be used as well to separate n-wells 104from p-wells 105. In some instances, even air gaps may be used asinsulating media and thus formed inside trenches 106 and the air gapsmay function as an insulator. Any excess of insulating materials 107that may be left on top of substrate 101 during the process ofdepositing into trenches 106 may be removed through, for example, achemical-mechanic-polishing (CMP) process.

FIG. 14 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 13, according to one embodiment of presentinvention. More specifically, a CMP process is applied to remove excessinsulating materials 107 on top of substrate 101. In together with theremoval of material 107, nitride hard-mask 112 b as well as underneathoxide layer 111 may be removed to expose underneath substrate 101,thereby creating well-isolation 108 and a top planar surface for furtherprocessing such as, for example, for forming fin-type transistors.

FIG. 15 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells according to anotherembodiment of present invention. More specifically, similar to theembodiment illustrated in FIG. 2, in order to form structure 200,embodiments of present invention may include forming an optional oxidelayer 211 and subsequently a nitride hard-mask layer 212 on top ofsubstrate 101 which has fin structures 102 and insulating structures 103formed therein. However, different from the embodiment in FIG. 2,instead of forming a poly hard-mask 113 on top of nitride hard-mask 112,nitride hard-mask layer 212 may be formed to have a thickness around,for example, 55˜65 nm that is thicker than, and sometimes twice as thickas, nitride hard-mask 112 illustrated in FIG. 2. Nitride hard-mask layer212 is later formed into a nitride hard-mask 214 (FIG. 20), as beingdescribed below in more details, without the use of a poly hard-masklayer as in the previous embodiment illustrated in FIG. 2.

FIG. 16 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 15, according to one embodiment of presentinvention. More specifically, a photo-resist layer may be formed suchas, for example, through a spin-on process on top of nitride hard-mask212, and the photo-resist layer may subsequently be formed into a firstresist-mask 221 through a photolithographic patterning process.Resist-mask 221 may represent a pattern wherein regions of substrate 101to be formed into, for example, negative-type wells (NW) are exposed andregions to be formed later into positive-type wells (PW) are covered byresist-mask 221. In other words, resist-mask 221 may be used as anion-implanting mask for forming, in the illustrated embodiment, NWs. Asa person skilled in the art will appreciate, the order of forming NW andPW may be reversed and PW may be formed first using a similar process.

Moreover, resist-mask 221 may be used as a mask in partially etchingunderneath nitride hard-mask layer 212 in a process of transforminghard-mask layer 212 into a hard-mask 214. Nitride hard-mask layer 212 ismade to preferably have a thickness that is at least twice a thicknessthat is suitable as a mask in a later deep trench etching process. Forexample, if a nitride hard-mask of 30 nm in thickness is needed for thelater formation of deep trenches, nitride hard-mask layer 212 may bemade to have a thickness of at least 60 nm. The depth of deep trenchesmay also dictate the required thickness of the hard-mask depending on arelative difference in etching ratio between substrate 101 and thehard-mask layer 212.

FIG. 17 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 16, according to one embodiment of presentinvention. More specifically, resist-mask 221 may be used in an etchingprocess to remove partially nitride hard-mask layer 212 that are notcovered, therefore exposed, by resist-mask 221. The removal may be madethrough, for example, a RIE process that is selective to photo-resistmaterial. In other words, the RIE process may remove a top portion ofthe exposed nitride hard-mask layer 212 without substantially affectingresist-mask 221. According to one embodiment, the etching process mayremove preferably about one half of the total thickness of nitridehard-mask layer 212. However, embodiment of present invention is notlimited in this aspect, and the portion of removed nitride hard-masklayer 212 may vary ranging, for example, about 30 to 70 percentages ofthe total thickness of nitride hard-mask layer 212. In anotherembodiment, the amount of nitride hard-mask layer 212 being removed maydepend upon the amount of thickness being left after the removal. Forexample, in one embodiment, the amount of thickness left may be made noless than 20 nm. The partial removal of nitride material from hard-masklayer 212 creates a modified nitride hard-mask layer 213 with recesses213 a therein. It is to be noted that this step of partially etchingnitride hard-mask layer 212 may be performed after the next step, asbeing described below in more details with reference to FIG. 18, ofion-implantation.

FIG. 18 is a demonstrative illustration of a step of a method of formingwells and isolations surrounding the wells, following the stepillustrated in FIG. 17, according to one embodiment of presentinvention. More specifically, using resist-mask 221, ion-implantationmay be performed to implant negative ions, such as P⁻ and As⁻, intosubstrate 101 to form regions of negative-wells 204. Optionally, thision-implantation step may be performed before the step illustrated inFIG. 17, before thickness of the resist-mask 221 may be thinned duringthe etching of nitride hard-mask layer 212, even though such thinning isassumed to be small because of the selectivity of etchant used.

FIG. 19 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 18, according to one embodiment of presentinvention. More specifically, the method may include stripping offresist-mask 221 and subsequently forming a second resist-mask 222 in therecesses 213 a formed inside nitride hard-mask layer 213. The secondresist-mask 222 may substantially fill in, but not entirely, recesses213 a in the modified nitride hard-mask layer 213, creating gaps 213 bbetween the edge of recesses 213 a and the second resist-mask 222. Thegaps 213 b may represent a width of well isolations to be formed betweenn-well (NW) and p-well (PW) later in substrate 101. This secondresist-mask 222 may be formed through, for example, any well-knownphotolithographic patterning processes. According to one embodiment, increating this second resist-mask 222, a mask pattern complementary tothe one used in creating first resist-mask 221 may be used after thepattern size being properly scaled to leave the necessary gaps 213 b asbeing described above.

FIG. 20 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 19, according to one embodiment of presentinvention. More specifically, the method may include subjecting theexposed portion of the modified nitride hard-mask layer 213 to adirectional selective etching process, such as a RIE process. Theetching process may further deepen the gaps 213 b between the edges ofthe recesses 213 a and the second resist-mask 222 until underneath oxidelayer 211, if any, or substrate 101 is exposed. The etching process mayalso lower the height of modified hard-mask layer 213 in areas that werepreviously covered by first resist-mask 221. As a result, a nitridehard-mask 214 is formed which has openings 214 a that are self-alignedto underneath regions of substrate 101 to be formed into well-isolationslater.

FIG. 21 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 20, according to one embodiment of presentinvention. For example, ion-implantation may be performed at this stageto form regions of substrate 101 that are not covered by secondresist-mask 222 into, for example, positive-type wells (PW). In otherwords, embodiment of present invention applies resist-mask 222 asion-implantation mask to implant positive ions, such as B⁺ and Ga⁺, intoregions of substrate 101. The formed PWs may have an overlapping regionswith the previously formed NWs in areas that are self-aligned to theopenings 214 a of nitride hard-mask 214. It is to be noted here that thestep of ion-implantation illustrated herein may be performed before thestep illustrated in FIG. 20 before the creation of nitride hard-mask214.

FIG. 22 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 21, according to one embodiment of presentinvention. Following the formation of both NWs and PWs in substrate 101,resist-mask 222 may be removed through, for example, a stripping processto expose underneath portions of hard-mask 214. The removal ofresist-mask 222 may be optional at this stage if it does not affect theetching of substrate 101 in the next step in forming deep trenches thatseparate NWs and PWs in substrate 101.

FIG. 23 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 22, according to one embodiment of presentinvention. More specifically, a selective etching process may be appliedto etch and create deep trenches 206 inside substrate 101 which isself-aligned to the edges of NWs and PWs provided the openings 214 a inthe nitride hard-mask 214. Openings 214 a are self-aligned to the edgesof NWs and PWs because of the nature of their creation as beingdescribed above.

FIG. 24 is a demonstrative illustration of a step of a method of formingwells and isolation surrounding the wells, following the stepillustrated in FIG. 23, according to one embodiment of presentinvention. Following the creation of deep trenches 206, insulatingmaterials such as low-k dielectric, oxide, or nitride material may beused in filling in the trenches to form well-isolations 208. In someembodiments, air gaps may be built in as part of isolation media. Anyexcess of insulating materials, together with nitride hard-mask 214 andunderneath oxide layer 211 may be removed through, for example, a CMPprocess.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the spirit ofthe invention.

What is claimed is:
 1. A method comprising: etching a top portion of ahard-mask layer in areas not covered by a first resist-mask to create arecessed portion of the hard-mask layer, the hard mask layer is on topof a substrate, and the first resist-mask is on top of a first portionof the hard-mask layer; using the first resist-mask in forming a firsttype of wells in a first region of the substrate; forming a secondresist-mask on top of a second portion of the hard-mask layer wherein afirst portion of the recessed portion of the hard-mask layer is coveredby the second resist-mask; etching a second portion of the recessedportion of the hard-mask layer that is not covered by the secondresist-mask until the substrate is exposed; using the second resist-maskin forming a second type of wells in a second region of the substrate;etching at least the exposed portion of the substrate to create deeptrenches that separate the first type of wells from the second type ofwells; and filling the deep trenches with insulating materials.
 2. Themethod of claim 1, wherein forming the second resist-mask on top of thesecond portion of the hard-mask layer comprises: forming the secondresist-mask in a region not previously covered by the first resist-mask,the second portion of the hard-mask layer being separated by gaps fromand not adjacent to the first portion of the hard-mask layer.
 3. Themethod of claim 2, wherein forming the first type of wells in the firstregion of the substrate comprises: performing a first ion-implantationin the first region of the substrate that is not covered by the firstresist-mask.
 4. The method of claim 3, wherein forming the second typeof wells in the second region of the substrate comprises: performing asecond ion-implantation in the second region of the substrate that isnot covered by the second resist-mask, the second type of wells havingoverlapping regions with the first type of wells in areas correspondingto the gaps.
 5. The method of claim 1, wherein etching the secondportion of the recessed portion of the hard-mask layer furthercomprises: etching a portion of the hard-mask layer that is previouslycovered by the first resist-mask and not recessed.
 6. The method ofclaim 1, wherein the second portion of the recessed portion of thehard-mask layer substantially aligns with areas overlapped by the firstand second regions of the substrate.
 7. The method of claim 1, whereinthe hard-mask layer is a nitride hard-mask layer and wherein etching thetop portion of the hard-mask layer comprises etching substantially closeto one half of a thickness of the hard-mask layer.